Reconstruction of neural function in advanced neurodegenerative conditions such as Alzheimer's disease, Parkinson's disease, ALS (amyotrophic lateral sclerosis) and the like requires replacement of the neural cells lost by cell death. Although neural cell transplantation has been attempted in animal experiments using embryonic or adult neural stem cells, ES cells and embryonic neural cells, such uses face major hurdles against their application in humans. Ethical issues surround the use of embryonic stem cells or neural cells, and the question of guaranteeing a stable supply is also a concern. The demonstrated ability of ES cells to differentiate is currently attracting much attention, but in addition to the numerous ethical issues, the cost and labor required to induce differentiation to specific cell types and the risk of forming teratoid tumors after transplantation are factors impeding stable application of this technology. In order to use adult neural stem cells, they must be extracted by craniotomy since they are found in a very limited core section of the central nervous system, and thus patients undergoing regenerative treatment are also exposed to a tremendous risk and burden.
Although approximately 10 years have passed since isolation of central nervous system stem cells in vitro, it has not yet been possible by the currently accepted protocols to differentiate neural stem cells and obtain large amounts of functional dopaminergic or cholinergic neurons (Lorenz Studer, Nature Biotechnology Dec. Issue, p. 117(2001).
A research group led by Professors Samuel Weiss of Calgary University (Canada) and Tetsuro Shingo has achieved success in efficiently inducing differentiation of dopamine-producing neural cells by administering a mixture of several tyrosine hydroxylase inducing factors (TH cocktail) into mice brains, but no previous example exists of inducing differentiation of dopaminergic neurons and cholinergic neurons from bone marrow stromal cells as according to the present invention.
Motor neurons are acetylcholinergic, and their application to such intractable diseases as ALS (amyotrophic lateral sclerosis) has been considered. In ALS, death of spinal marrow motor neurons for reasons as yet unknown leads to loss of muscle controlling nerves, thereby preventing movement of muscles throughout the body including the respiratory muscles, and leading to death of the patient within 2-3 years after onset. Currently, no effective treatment exists for this condition, but rat ALS models are being established.
Most degenerative muscular diseases such as muscular dystrophy are progressive, and therefore transplantation of skeletal muscle cells may constitute an effective treatment. In healthy individuals, satellite cells present in muscle tissue supplement for skeletal muscle that has lost its regenerative capacity, but in progressive muscular diseases the number of such cells is reduced and regenerative capacity is accordingly lower. Thus, while transplantation of skeletal muscle or its precursor cells can be used as treatment, no effective curative means yet exists.
In the course of development of the central nervous system, neurons and glial cells are induced to differentiate from relatively homogeneous neural precursor cells or neural stem cells. A mechanism is in place whereby some of the cells in the precursor cell population differentiate to certain cell subtypes in response to differentiation signals, while the other cells remain undifferentiated. Specifically, previously differentiated cells send out certain signals to their surrounding cells to prevent further differentiation to cells of their own type. This mechanism is known as lateral inhibition. In Drosophila, cells already differentiated to neurons express the “Delta” ligand while their surrounding cells express the Delta receptor “Notch”, and binding of the ligand with receptor ensures that the surrounding cells do not differentiate to neural cells (Notch signaling). The Delta-Notch system appears to function in spinal cord cells as well (see, for example, Chitnis, A., Henrique, D., Lewis, J., Ish-Horowicz, D., Kintner, C.: Nature, 375, 761-766(1995)).
It is thought that cellular interaction via the membrane protein Notch plays a major role in the development process whereby a homogeneous cell group produces many diverse types, and specifically, that upon ligand stimulation by adjacent cells, Notch induces expression of HES1 or HES5 which inhibit bHLH (basic helix-loop-helix) neurodifferentiation factors such as Mash1, Math1 and neurogenin, to suppress differentiation to the same cell type as the adjacent cell (see, for example, Kageyama et al., Saibo Kogaku [Cell Engineering] Vol. 18, No. 9, 1301-1306(1999)).
The Notch intracellular pathway is currently understood as follows. When Notch is first activated by ligands on the surface of adjacent cells (Delta, Serrate, Jagged), its intracellular domain is cleaved off (Artavanis-Tsakonas S. et al.: Science (1999)284:770-776 and Kageyama et al., Saibo Kogaku [Cell Engineering] Vol. 18, No. 9, 1301-1306(1999)). After cleavage of the intracellular domain of Notch, it migrates from the cell membrane to the nucleus with the help of a nuclear localization signal (NLS) and in the nucleus forms a complex with the DNA-binding protein RBP-Jκ (Honjo T.: Genes Cells (1996) 1:1-9 and Kageyama et al., Saibo Kogaku [Cell Engineering] Vol. 18, No. 9, 1301-1306(1999)). RBP-Jκ itself is a DNA-binding repressor of transcription, and in the absence of activated Notch it binds to the promoter of the HES1 gene, which is a differentiation inhibiting factor, thereby blocking its expression; however, once the complex forms between RBP-Jκ and the intracellular domain of Notch, the complex acts instead to activate transcription of the HES1 gene (see Jarriault S. et al.: Nature (1995) 377:355-358, Kageyama R. et al.: Curr. Opin. Genet. Dev. (1997) 7:659-665 and Kageyama et al., Saibo Kogaku [Cell Engineering] Vol. 18, No. 9, 1301-1306(1999)). This results in expression of HES1 and HES1-induced suppression of differentiation. In other words, Notch is believed to suppress differentiation via HES1 (see Kageyama et al., Saibo Kogaku [Cell Engineering] Vol. 18, No. 9, 1301-1306(1999)).
In mammals as well, it has become clear that Notch-mediated regulation of gene expression is important in maintaining neural precursor cells or neural stem cells and in the highly diverse process of neural differentiation, and that the Notch pathway is also essential for differentiation of cells other than those of the nervous system (see Tomita K. et al.: Genes Dev. (1999) 13:1203-1210 and Kageyama et al., Saibo Kogaku [Cell Engineering] Vol. 18, No. 9, 1301-1306(1999)). In addition, the existence of a HES-independent Notch pathway, negative regulation of Notch signaling on the transcription level and negative interaction on the protein level have also been anticipated (see Goh, M., Saibo Kogaku [Cell Engineering] Vol. 18, No. 9, 1291-1300(1999)). Still, all of the aforementioned publications either teach or suggest that Notch signaling acts in a direction which suppresses differentiation.
Central nervous disorders in which reconstruction is not an option actually include a variety of different conditions with a high incidence rate in the population, from injury-induced spinal damage or cerebrovascular impairment or glaucoma which leads to blindness, to neurodegenerative conditions such as Parkinson's disease. Research on neuroregenerative methods to treat such diseases is therefore an urgent social need, and the results of this research by the present inventors is believed to be a breakthrough for application to humans. Bone marrow stromal cells are easily extracted by bone marrow aspiration on an outpatient basis, and due to their highly proliferative nature they can be cultured in large amounts within a relatively short period. Moreover a tremendous advantage may be expected since autologous transplantation can be carried out if nerves are formed from one's own bone marrow stem cells. The lack of immunological rejection would dispense with the need for administering immunosuppressants, thus making safer treatment possible. Furthermore, since bone marrow stem cells can be obtained from a bone marrow bank, this method is realistically possible from a supply standpoint. If such cells can be used to derive neural cells, for which no effective means has heretofore existed, then a major effect may be expected in the field of regenerative medicine.
ALS (amyotrophic lateral sclerosis) is a condition in which cell death of spinal marrow motor neurons for reasons as yet unknown leads to loss of muscle controlling nerves, thereby preventing movement of muscles throughout the body including the respiratory muscles and leading to death of the patient within 2-3 years after onset, but at the current time no effective treatment exists. Formation of acetylcholinergic neurons from one's own bone marrow stem cells would allow autologous transplantation, and this would offer a major benefit that might even serve as a cure for ALS.
Effective treatment methods also currently do not exist for muscular diseases such as muscular dystrophy, a degenerative disease of the skeletal muscle. A major benefit would also be afforded for such conditions, since formation of skeletal muscle cells from one's own bone marrow stem cells would allow autologous transplantation. Using such cells to derive skeletal muscle cells, for which no effective means has heretofore existed, would also be expected to provide a major effect in the field of regenerative medicine.
The possible applications of this technology are not only in the field of clinical treatment but also in the area of engineering of artificial organs and the like, which is expected to be an important field of development in the future. If neural cells or muscle cells could be easily produced on a cell culturing level, then applications may be imagined for creation of hybrid artificial organs and the like.